Raheem Sterling’s quick-fire second-half hat-trick sent Manchester City four points clear at the top of the Premier League, but there was controversy over the opener that broke down a stubborn Watford side.

With the game goalless at the start of the second half, Sterling was challenged by Daryl Janmaat as he ran on to Sergio Aguero’s flick and the ball cannoned off him and into the net.

Sterling was clearly offside when Aguero chested the ball into his path and the lineman’s flag went up. But, after a long discussion with his fellow official, referee Paul Tierney overruled his decision, to the disbelief of the Hornets players.

There was no disputing the legality of Sterling’s second goal, which came only four minutes later when he tapped in Riyad Mahrez’s cross at the far post after a flowing City move.

And, just before the hour mark, the 24-year-old England forward made it 3-0, running on to a David Silva pass and cutting past two defenders before slotting home his 18th goal of the season. Raheem Sterling’s three goals against Watford came in the space of just 13 second-half minutes.

Watford, who had made seven changes ahead of their FA Cup quarter-final with Crystal Palace next weekend, belatedly threw on Troy Deeney and Gerard Deulofeu – two of those to be left out.

The pair combined seconds later to pull a goal back with their first touches when Deeney flicked on a long ball for Deulofeu to fire home with his side’s first shot at goal, after 66 minutes.

It proved to be only a consolation rather than the start of an unlikely comeback, with City comfortably holding on to clinch their sixth successive league win.

Their four-point lead is their biggest advantage at the top since 4 December, although Liverpool can cut the gap when they host Burnley on Sunday.